Do you seriously believe that this is a binary situation, that Ukraine's only alternatives are capitulation or the defeat of Russia? What makes you think that putin is NOT interested in taking all Ukraine, that he will ever respect a peace deal that he signs, that he won't just use a cease fire to rearm for another invasion, as he has done in Ukraine already?

Russia leaving Ukraine is not the same as Russia being defeated. Russia pulling back to its borders leaves Russia intact, not under attack, and no longer committing daily war crimes. Russian military presence in Ukraine is a war crime. Should someone be insane enough to invade Russia THEN Russia will be justified in raising security concerns.